This project is focused on understanding the molecular and cellular basis of neuronal migration. Many types of neurons undergo migration to reach their appropriate destination by responding to both contact-dependent and contact-independent signals;aberrant neuronal migration underlies a variety of birth defects. Neuronal migration is influenced by cell adhesion molecules, which play a dual role allowing neurons to engage in cellular interactions that influence migration as well as regulating signaling mechanisms important for the outgrowth and guidance of neural projections. Preliminary experiments have shown that N-cadherin (Ncad), a prominent cell adhesion molecule in the nervous system, is required for facial branchiomotor neuron (FBMN) migration. The experiments outlined in this proposal aim to test the overarching hypothesis that Ncad is required for FBMN migration by modulating both adhesion-dependent interactions and the response to molecular guidance cues within the hindbrain environment. In Aim 1 a detailed analysis of neuronal migratory behavior in Ncad-deficient embryos will be performed using live imaging to explore how Ncad regulates FBMN migration and guidance. Further, cell transplantation will test whether Ncad functions autonomously or non-autonomously in FBMNs to mediate their migration. In preliminary experiments I find Ncad- depletion arrests FBMN migration and some neurons aberrantly migrate into the midline, suggesting an attractant midline cue guides FBMN migration. Aim 2 will test the hypothesis that Ncad modulates FBMN response to the molecular guidance cue SDF1a. This will be accomplished by using ectopic localization of SDF1a in wild type and Ncad-deficient embryos to test the ability of SDF1a to act as an attractant cue to FBMNs and to examine the role of Ncad in modulating the response of FBMNs to SDF1a. Lastly, another means of providing directional cues to neurons is through following pre-laid axon tracts, which relies upon the formation of cellular adhesions between neurons and the axon tract. Aim 3 will test the hypothesis that Ncad is required for adhesion-dependent interactions between the FBMNs and the medial longitudinal fascicle (MLF) to facilitate FBMN migration. To examine the dynamic interaction between facial neurons and the MLF I will utilize immuno- fluorescence and time-lapse microscopy in wild type and Ncad-deficient embryos. I will also investigate the importance of the MLF in facial neuron guidance by removing the MLF using surgical manipulations. These experiments will test the importance of Ncad in regulating adhesion-dependent interactions between FBMNs and the MLF. Together the aims of this proposal will determine the role of Ncad in neuronal migration and guidance and add to our understanding of how neuronal migration is regulated. PUBLIC HEALTH RELEVANCE: Neuronal migration is critical for the ability of neurons to navigate their environment to reach their proper target. Understanding how neurons migrate is important because defects in neuronal migration result in human neurological diseases, most commonly encompassing mental retardation, epilepsy and autism. The proposed experiments will extend our current knowledge of the molecular and cellular basis of neuronal migration.